Measurement device including an electrode head with an anchor formed on an outer peripheral portion

ABSTRACT

A measurement device comprises: a container  1  including an aperture  6   a ; a lining  2  applied to an inner surface of the container  1 ; an electrode  3  provided in the aperture, and a spring  7  biasing the electrode  3  in a direction from the inside to the outside of the container  1 . The electrode  3  includes: an electrode head  3   a ; an anchor  4  formed on an outer peripheral portion of the electrode head  3   a ; an electrode shaft  3   b  formed integrally with the electrode head  3   a ; and an electrode tapered portion  5  tapered with its diameter gradually reduced from the anchor  4  to the electrode shaft so as to fit in the aperture. The electrode  3  is inserted from the inside of the container  1  so as to expose a part of the electrode shaft  3   b  out of the container  1.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2008-019550 filed on Jan. 30, 2008, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a measurement device for measuringvarious features, state quantities and the like of measurement targetssuch as liquids, gases or powders. More specifically, the presentinvention relates to a measurement device provided with an electrodemounting structure having an excellent sealing property.

2. Description of the Related Art

An electromagnetic flow meter configured to measure a flow rate of aliquid has been known as a conventional measurement device for measuringa physical quantity. The electromagnetic flow meter measures the flowrate by applying an electric current to a coil to generate a magneticfield inside a measurement pipe, then by picking up, with an electrode,an electromotive force generated in proportion to the electricconductivity of the liquid flowing inside the measurement pipe, and thenby detecting the magnitude of the electromotive force. Generally, aresin lining formed of fluororesin, polyurethane resin or the like isapplied to an internal surface of the measurement pipe of thiselectromagnetic flow meter in order to prevent corrosion.

The electrode used in this electromagnetic flow meter is in directcontact with a measurement target. In general, two types of structuresare known as the structure of this electrode. These structures arecalled an external insertion type and an internal insertion type,respectively. In the external insertion type, an electrode is insertedinto the inside of the container from the outside of the container inwhich a measurement target is to flow or be sealed. The electrode ispressed against the container from the outside by use of a spring andthe like to ensure a sealing property of the container (see JapanesePatent Application Laid-Open Publications Nos. 2003-262544, 04-95719 and2004-163193). In the internal insertion type, the electrode is insertedfrom the inside to the outside of a container, and the electrode ispulled outwardly from the outside of the container by use of a spring.In this way, an electrode head is closely attached to the container, andthe sealing property of the container is thereby ensured (see JapanesePatent Application Laid-Open Publications Nos. 11-83569, 04-198816 (FIG.2A), 2007-240231, 04-95819, and 03-55865).

SUMMARY OF THE INVENTION

As described above, the electrode of the above-described externalinsertion type is pressed from the outside by use of the spring or thelike to ensure the sealing property. Accordingly, if a biasing force ofthe spring is weakened by aging or other factors, the force to press theelectrode against internal pressure of the container is also weakened.As a consequence, the sealing property is damaged, and the measurementtarget leaks out of the container.

Moreover, in the electrode of the external insertion type, a sealingproperty retainer (a sealing unit) is not constituted by the electrodehead that is in direct contact with the measurement target inside thecontainer, but by an O-ring or a gasket located in a position close tothe outside of the container. Therefore, the measurement targetpermeates the sealing property retainer. As a result, if the measurementtarget possesses a corrosive property, the electrode is corroded byformation of an oxygen concentration cell or the like at a portion wherethe measurement target permeates. If the measurement target possesses aprecipitation property, the measurement target precipitates at theportion where the measurement target permeates, thereby spreading a gapbetween the container and the electrode, and thus destroying the sealingproperty of the container.

Further, in the case of the electrode of the external insertion type,the electrode is pressed from the outside of the container by use of thespring, and it is therefore necessary to provide a wall for holding thespring (which is generally called a boss). Accordingly, there is aproblem of an increase in a process cost by an amount needed to attachthis boss to the container by welding or the like.

On the other hand, in the case of the electrode of the internalinsertion type, the electrode head is closely attached to the innersurface of the container by pulling the electrode outwardly by using thespring located on the outside. The sealing property is even improved bythe internal pressure of the container that presses the electrode head.Therefore, the electrode of the internal insertion type has an advantagein achieving a favorable sealing property. Nevertheless, according tothe technique disclosed in Japanese Patent Application Publication No.Hei 11-83569, there is a problem that a gasket, which is placed betweentapered portions respectively formed on the container and on theelectrode, melts if the measurement target possesses a corrosiveproperty.

Meanwhile, according to the technique disclosed in Japanese PatentApplication Laid-Open Publication No. 04-198816, a sealing propertyretainer is formed by means of area sealing which is established bycontact between a tapered portion provided on the electrode and atapered portion provided on the container. Therefore, if the resinlining provided on the inner surface of the container is made ofrelatively hard resin such as fluororesin, it is not possible to obtainand maintain contact pressure necessary for retaining the sealingproperty.

Meanwhile, according to the technique disclosed in Japanese PatentApplication Laid-Open Publication No. 2007-240231, as shown in FIGS. 1Aand 1B as well as FIGS. 2A and 2B, a protrusion 31 having a semicircularcross section is provided around an outer peripheral portion of anelectrode head 30 of an electrode 36, on the opposite side to a surfacethat is in contact with the measurement target. In this structure, asealing property retainer is not located on a wide area, but isconcentrated on a narrow area. Moreover, by pulling up the sealingproperty retainer with a spring 32, the contact pressure necessary forretaining the sealing property can be obtained even when a lining 34provided on an inner surface of a container 33 is made of relativelyhard resin such as fluororesin. Here, FIG. 1A shows a cross-sectionalview including an axial direction of the container 33 shown in FIG. 1B.FIG. 2A shows a cross-sectional view including a diametrical directionof the container 33 shown in FIG. 2B.

In this technique, a flat surface exists between an electrode shaft 35and the protrusion 31. Accordingly, in a cross section S1 (see FIG. 1B)in the axial direction as shown in FIG. 1A, this flat surface is closelyattached to the container. However, the container 33 has a circular formin a cross section S2 (see FIG. 2B) in the diametrical direction asshown in FIG. 2A. Therefore, this technique has a problem that thesealing property is lost because a gap is formed between this flatsurface and the inner surface of the cylindrical container 33.

Further, according to the technique disclosed in Japanese PatentApplication Laid-Open Publication No. 04-95819, an electrode head isburied in a container, and a sealing property retainer is a sealingmember located deeper than the electrode head. As is similar to theelectrode of the external insertion type, this configuration hasproblems of corrosion of the electrode attributable to an oxygenconcentration cell, damage of the sealing property by a depositedmaterial, and melting of the sealing member by corrosion.

Moreover, according to the technique disclosed in Japanese ExaminedUtility Model Application Publication No. 03-55865, an electrode head isformed to have a flat surface. Therefore, if the resin lining providedon the inner surface of the container is made of relatively hard resinsuch as fluororesin, it is difficult to obtain contact pressurenecessary for retaining the sealing property. Moreover, since thecontainer is formed into a circular shape in its cross section in thediametrical direction, a gap is formed between the flat surface of theelectrode head and the inner surface of the cylindrical container, whichdamages the sealing property.

The present invention has been made for solving the above-describedproblems. An object of the present invention is to provide a low-costmeasurement device provided with an electrode mounting structure havingan excellent sealing property.

An aspect of the present invention provides a measurement devicecomprising: a container in which a measurement target flows or issealed, the container including an aperture; a lining which is appliedto an inner surface of the container; an electrode provided in theaperture; and a spring configured to bias the electrode in a directionfrom the inside to the outside of the container; wherein the electrodeincludes: an electrode head provided with a first surface, which isexposed to the inside of the container and is in contact with themeasurement target, and a second surface located on an opposite side tothe first surface; an anchor formed on an outer peripheral portion ofthe electrode head so as to protrude from the second surface and to beburied in the lining; an electrode shaft formed integrally with theelectrode head so as to extend toward the opposite side of the firstsurface; and an electrode tapered portion tapered with its diametergradually reduced from the anchor to the electrode shaft so as to fit inthe aperture; and wherein the electrode is inserted from the inside ofthe container so as to expose a part of the electrode shaft out of thecontainer.

The first surface may be formed into any of a semispherical shape and aflat shape.

The anchor may be formed into any of a semicircular shape and atriangular shape in its cross-section including an axis of theelectrode.

A V-shaped groove may be formed on a surface of the electrode taperedportion in a circumferential direction of the electrode tapered portion.

The measurement device may further comprise a sealing member. Theaperture may further include a tapered portion tapered with its diametergradually reduced from an outer surface to the inner surface of thecontainer, and the sealing member may be fitted to the tapered portionon the aperture and be biased from the outside to the inside of thecontainer by the spring.

According to the present invention, a low-cost measurement deviceprovided with an electrode mounting structure having an excellentsealing property, can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of an electrode and its surroundingpart of a conventional electromagnetic flow meter. FIG. 1B is a viewschematically showing a position of the cross section shown in FIG. 1A.

FIG. 2A is a cross-sectional view of an electrode and its surroundingpart of another conventional electromagnetic flow meter. FIG. 2B is aview schematically showing a position of the cross section shown in FIG.2A.

FIG. 3 is a schematic drawing showing the principle of anelectromagnetic flow meter serving as a measurement device according toa first embodiment of the present invention.

FIG. 4 is an external perspective view of the electromagnetic flowmeter.

FIG. 5 is a cross-sectional view of structures of an electrode and itssurrounding part according to the first embodiment of the presentinvention.

FIG. 6 is an external perspective view of the electrode according to thefirst embodiment of the present invention.

FIG. 7 is a cross-sectional view of structures of an electrode and itssurrounding part according to a second embodiment of the presentinvention.

FIG. 8 is a cross-sectional view of structures of an electrode and itssurrounding part according to a third embodiment of the presentinvention.

FIG. 9 is a cross-sectional view of structures of an electrode and itssurrounding part according to a fourth embodiment of the presentinvention.

FIG. 10 is a cross-sectional view of structures of an electrode and itssurrounding part according to a fifth embodiment of the presentinvention.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be describedbelow in detail with reference to the accompanying drawings. It is to benoted that an electromagnetic flow meter will be used in the followingdescription as an example of a measurement device that includes anelectrode mounting structure of the present invention.

First Embodiment

As shown in FIG. 3, in an electromagnetic flow meter according to afirst embodiment of the present invention, a measurement pipe 1 throughwhich a fluid as a measurement target flows, is provided with a pair ofcoils 21 a and 21 b which are located to face each other. Themeasurement pipe 1 is made of metal or insulator such as ceramicmaterial or the like. Moreover, a pair of electrodes 3A and 3B that faceeach other are provided orthogonally to the pair of coils 21 a and 21 b.

An excitation current is supplied from an excitation unit 22 to the pairof coils 21 a and 21 b. The excitation unit 22 generates the excitationcurrent corresponding to a square-wave timing signal sent from a timingcircuit 23 and transmits the current to the pair of coils 21 a and 21 bas described previously. The timing circuit 23 is formed of amicrocomputer, for example, and is configured to generate thesquare-wave timing signal for defining measurement timing and sends thesignal to the excitation unit 22 and to a flow rate operating unit 25.

Signals detected by the pair of electrodes 3A and 3B are sent to asignal processor 24. The signal processor 24 performs processing, suchas amplification and noise filtering, with the signals sent from thepair of electrodes 3A and 3B, then detects a potential differencebetween the signals, converts the potential difference into a digitalsignal, and sends the digital signal to the flow rate operating unit 25.In response to the timing signal sent from the timing circuit 23, theflow rate operating unit 25 calculates a flow rate based on the signalsent from the signal processor 24, and sends a signal indicating theflow rate to a display unit 26. The display unit 26 is formed of an LCD(liquid crystal display), for example, and is configured to display theflow rate in response to the signal indicating the flow rate which issent from the flow rate operating unit 25.

Next, operations of the electromagnetic flow meter having the aboveconfiguration will be described. First, the timing circuit 23 generatesa timing signal at predetermined measurement timing and sends the timingsignal to the excitation unit 22 and to the flow rate operating unit 25.The excitation unit 22 generates an excitation current in response tothe timing signal sent from the timing circuit 23 and sends theexcitation current to the pair of coils 21 a and 21 b. Thereby, amagnetic field is generated between the coil 21 a and the coil 21 binside the measurement pipe 1. The measurement target fluid flows inthis magnetic field and cuts a magnetic flux, whereby an electromotiveforce is generated in the measurement target fluid. Signals indicatingthe electromotive force thus generated in the measurement target fluidare sent to the signal processor 24 through the pair of electrodes 3Aand 3B.

The signal processor 24 detects the magnitude of the electromotive forceby calculating a potential difference between the signals sent from thepair of electrodes 3A and 3B, converts the potential difference into adigital signal, and sends the digital signal to the flow rate operatingunit 25. In response to the timing signal sent from the timing circuit23, the flow rate operating unit 25 calculates a flow rate based on thesignal sent from the signal processor 24, and sends a signal indicatingthe flow rate to the display unit 26. The display unit 26 displays theflow rate in response to the signal indicating the flow rate which issent from the flow rate operating unit 25.

As shown in FIG. 4, flanges 1 a and 1 b are provided on both ends of themeasurement pipe 1 so as to be connected to pipes (not shown). Moreover,an electrode unit 20 containing the electrode 3A is provided almost inthe center of the measurement pipe 1. Here, the electromagnetic flowmeter also includes an electrode unit for containing the electrode 3B.However, FIG. 4 shows just one of the electrode units 20.

As shown in FIG. 5, the electrode unit 20 includes the electrode 3, aspring 7, spacers 8, and a nut 9. FIG. 6 is an external perspective viewof the electrode 3.

The measurement pipe 1, which serves as a container in which themeasurement target is to flow or be sealed, is provided with an aperture6 a. The aperture 6 a includes a container tapered portion 6 which istapered with the diameter gradually reduced from an inner surface of themeasurement pipe 1 toward an outer surface thereof. A lining 2 isattached to the inner surface and the aperture 6 a of the measurementpipe 1 so as to prevent the measurement pipe 1 from corrosion by themeasurement target. The electrode 3 is inserted from the inside of themeasurement pipe 1 to this aperture 6 a.

The electrode 3 includes an electrode head 3 a and an electrode shaft 3b that continues to this electrode head 3 a. The electrode head 3 a isexposed to the inside of the measurement pipe 1 and provided with asurface which is in direct contact with the measurement target. Screwthreads 3 c are formed over a portion of the electrode shaft 3 b locatedoutside the measurement pipe 1, and the nut 9 is screwed onto thesescrew threads 3 c. A surface of the electrode head 3 a which is incontact with the measurement target, i.e. a surface exposed to theinside of the measurement pipe 1 (a first surface: a vertex) is formedinto a semispherical shape that protrudes to the inside of themeasurement pipe 1.

An anchor 4 is formed on the outer periphery of the electrode head 3 a,which is the opposite surface (a second surface) to the surface incontact with the measurement target. The anchor 4 is a protrusion. Thisprotrusion is formed so as to have a semicircular shape smaller than aradius of the electrode shaft 3 b in its cross section including an axisof the electrode 3.

Moreover, an electrode tapered portion 5 is provided over a portionbetween the anchor 4 at the electrode head 3 a and the electrode shaft 3b. The electrode tapered portion 5 is tapered with the diametergradually reduced from the anchor 4 to the electrode shaft 3 b so as tofit into the container tapered portion 6 on the aperture 6 a.

While interposing the spring 7 sandwiched between the spacers 8, the nut9 is screwed onto the portion of the electrode shaft 3 b outside of themeasurement pipe 1, the electrode shaft 3 b being inserted from theinside of the measurement pipe 1. Thereby, the electrode 3 is alwaysbiased in the direction from the inside to the outside of themeasurement pipe 1.

In the first embodiment configured as described above, the portion ofthe electrode head 3 a exposed to the inside of the measurement pipe 1is formed into the semispherical shape. Therefore, when the measurementtarget flows inside the measurement pipe 1, this shape acts to increasea flow velocity of the measurement target at the vertex of the electrodehead 3 a.

The anchor 4 formed on the electrode head 3 a includes the semicircularprotrusion having a relatively small diameter. Accordingly, the anchor 4is easily buried into the lining 2 with a relatively small force to pullthe electrode 3 from the inside to the outside of the measurement pipe3. As a result, the anchor 4 establishes line sealing instead of facesealing and thereby acts to increase contact pressure.

Moreover, when the pressure inside the measurement pipe 1 increases andthus presses the electrode head 3 a, the electrode tapered portion 5 atthe electrode head 3 a is closely attached to the container taperedportion 6 at the measurement pipe 1 by way of the increased pressure. Inthis way, the contact pressure between the electrode tapered portion 5and the container tapered portion 6 is increased.

As described above, according to the first embodiment of the presentinvention, the electrode head 3 a increases the flow velocity of themeasurement target by forming its vertex into the semispherical shape.Therefore, it is possible to reduce adhesion or precipitation of themeasurement target on the electrode head 3 a and to reduce deposition ofthe measurement target on the electrode head 3 a.

Moreover, even when the lining 2 is made of relatively hard resin suchas fluororesin, the anchor 4 formed on the electrode head 3 a is easilyburied into the lining 2 with a small force. Therefore, it is possibleto obtain the contact pressure necessary for retaining the sealingproperty of the measurement pipe 1.

Further, when the pressure inside the measurement pipe 1 increases, sodoes the force to press the electrode head 3 a. The pressing forceaccordingly increases the force to press the electrode tapered portion 5of the electrode head 3 a to the container tapered portion 6. Therefore,the contact pressure between the electrode tapered portion 5 and thecontainer tapered portion 6 becomes stronger and the sealing property isthereby enhanced. As a result, a self-sealing function is achieved.

Moreover, the spring 7 always pulls the electrode 3 from the inside tothe outside of the measurement pipe 1. Accordingly, even if thethickness of the lining 2 changes due to aging or if the position of theelectrode 3 is displaced by variation in the force to press theelectrode head 3 a due to a change in the internal pressure of themeasurement pipe 1, it is possible to ensure and maintain the sealingproperty by causing the electrode 3 to follow the positional change.

Second Embodiment

As shown in FIG. 7, in a measurement device according to a secondembodiment of the present invention, the structure of the electrode head3 a of the electrode 3 of the first embodiment is changed. In thefollowing description, the same constituents as those in the firstembodiment are designated by the same reference numerals used in thefirst embodiment, and the description thereof will be omitted.

In the second embodiment, the electrode head 3 a is formed to have aflat surface that is exposed to the inside of the measurement pipe andis in direct contact with the measurement target (a first surface: avertex).

This second embodiment achieves operations and effects similar to thosein the first embodiment although the effects to prevent adhesion,precipitation and deposition of the measurement target may be reduced.Note that the second embodiment achieves exactly the same operations andeffects as those in the first embodiment provided that the measurementtarget does not possess an adhesion property, a precipitation propertyor a deposition property.

Third Embodiment

As shown in FIG. 8, in a measurement device according to a thirdembodiment of the present invention, the anchor 4 formed on theelectrode head 3 a of the electrode 3 according to the first embodimentis replaced by an anchor 4 a. In the following description, the sameconstituents as those in the first embodiment are designated by the samereference numerals used in the first embodiment, and the descriptionthereof will be omitted.

The anchor 4 a is formed into a triangular protrusion in its crosssection including the axis of the electrode 3.

In addition to the operations and effects similar to those in the firstembodiment, the third embodiment achieves, as an anchor effect, a highereffect than the first embodiment in retaining the sealed state.

In the third embodiment, the anchor 4 formed on the electrode head 3 aaccording to the first embodiment is replaced by the anchor 4 a.However, it is also possible to replace the anchor 4 formed on theelectrode head 3 a according to the second embodiment by the anchor 4 a.

Fourth Embodiment

As shown in FIG. 9, in a measurement device according to a fourthembodiment of the present invention, the electrode tapered portion 5 onthe electrode 3 according to the first embodiment is provided with aV-shaped groove 10 along a circumferential direction of the electrodetapered portion 5. In the following, the same constituents as those inthe first embodiment are designated by the same reference numerals usedin the first embodiment, and the description thereof will be omitted.

In the fourth embodiment, the lining 2 is buried into the V-shapedgroove 10. Accordingly, in addition to the operations and effectssimilar to those achieved by the first embodiment, the fourth embodimentfurther achieves a higher sealing property by way of the sealed surfaceformed between the electrode tapered portion 5 and the container taperedportion 6.

In the fourth embodiment, the V-shaped groove 10 is provided on theelectrode tapered portion 5 of the electrode head 3 a according to thefirst embodiment. However, the V-shaped groove 10 may also be providedon the electrode tapered portion 5 of the electrode 3 according to thesecond or third embodiment.

Fifth Embodiment

As shown in FIG. 10, a measurement device according to a fifthembodiment of the present invention is a modification of the fourthembodiment. In the following description, the same constituents as thosein the first embodiment are designated by the same reference numeralsused in the first embodiment and the description thereof will beomitted.

In the measurement device according to the fifth embodiment, theaperture 6 a of the measurement pipe 1 includes a secondary taperedportion 12 which is tapered with the diameter gradually reduced from theouter surface of the measurement pipe 1 toward the inner surfacethereof. The lining 2 is attached to a range from the inner surface ofthe measurement pipe 1 to a point between the container tapered portion6 and the secondary tapered portion 12. Moreover, one of the spacers 8is interposed between the secondary tapered portion 12 and the spring 7,and a sealing member (such as an O-ring) 11 is fitted thereto. Thesealing member 11 acts to prevent an inflow of gas permeating the liningand to retain the sealing property. The sealing member retains thesealing property of the container even if a gap is formed between theelectrode 3 and the lining 2. Specifically, for example, when themeasurement target leaks out as indicated by a dotted line A or when aliquid or a gas permeates the lining 2 as indicated by a dotted line B,it is possible to prevent further leakage of these materials.

In addition to the operations and effects similar to those achieved bythe fourth embodiment, the fifth embodiment can avoid further leakage ofthe liquid or the gas permeating the lining 2 or leakage of themeasurement target to the outside of the measurement pipe 1, themeasurement target accidentally having passed through the sealingproperty retaining structure provided on the electrode head 3 a.

In the fifth embodiment, the secondary tapered portion 12 is added tothe fourth embodiment so as to fit the sealing member 11 thereto.However, the secondary tapered portion 12 may also be added to any ofthe first to third embodiments so as to fit the sealing member 11thereto.

It is to be understood that the present invention is not limited only tothe electromagnetic flow maters according to the first to fifthembodiments. Although the container tapered portion 6 is formed on thecontainer 1 in the first to fifth embodiments, it is also possible toform only the electrode tapered portion 5 without forming the containertapered portion 6 on the container 1. Similar effects to those describedin the first to fifth embodiments are also obtained in this case.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a water mater, a gas meter, andso forth.

1. A measurement device comprising: a container in which a measurementtarget flows or is sealed, the container including an aperture; a liningwhich is applied to an inner surface of the container; an electrodeprovided in the aperture; a sealing member; and a spring configured tobias the electrode in a direction from the inside to the outside of thecontainer; wherein the electrode includes: an electrode head providedwith a first surface, which is exposed to the inside of the containerand is in contact with the measurement target, and a second surfacelocated on an opposite side to the first surface; an anchor formed on anouter peripheral portion of the electrode head so as to protrude fromthe second surface and to be buried in the lining; an electrode shaftformed integrally with the electrode head so as to extend toward theopposite side of the first surface; and an electrode tapered portiontapered with its diameter gradually reduced from the anchor to theelectrode shaft so as to fit in the aperture; and wherein the electrodeis inserted from the inside of the container so as to expose a part ofthe electrode shaft out of the container, wherein the aperture is formedwith a first tapered portion and a second tapered portion, the firsttapered portion is tapered from an outer surface of the container withits diameter gradually reduced from the outer surface to the innersurface of the container, and the second tapered portion is tapered froman inner surface of the container with its diameter gradually reducedfrom the inner surface to an outer surface of the container, and whereinthe sealing member is fitted to the first tapered portion on theaperture and is biased from the outside to the inside of the containerby the spring.
 2. The measurement device according to claim 1, whereinthe first surface is formed into any of a semispherical shape and a flatshape.
 3. The measurement device according to claim 1, wherein theanchor is formed into any of a semicircular shape and a triangular shapein its cross-section including an axis of the electrode.
 4. Themeasurement device according to claim 1, wherein a V-shaped groove isformed on a surface of the electrode tapered portion in acircumferential direction of the electrode tapered portion.
 5. Themeasurement device according to claim 1, wherein the sealing member isdisposed separately from the lining.